The current state of eDNA research in freshwater ecosystems: are we shifting from the developmental phase to standard application in biomonitoring?

Abstract

Environmental DNA (eDNA) has seen a massive increase in application in freshwater systems with a concurrent growth in protocol developments and a drive to gain a better understanding of the ‘ecology’ of eDNA. This raises the question of whether we are currently still in an early, developmental phase of eDNA-based assessments or already transitioning into a more applied stage for biomonitoring. I conducted a systematic literature review on 381 eDNA-focused studies in freshwater systems targeting macro-organisms over the last 5 years, assessing study goals, methods, target systems and taxa and study design aspects. The results show an increase of biomonitoring-focused studies throughout the years, while the fraction of studies investigating the ‘ecology’ of eDNA decreased. The application of metabarcoding significantly increased while studies applying qPCRs tentatively declined. A geographic inequality was observed concerning study numbers and study goals biased towards the global North. Descriptive studies increased, but the fraction of in-field studies and studies applying eDNA and conventional methods combined revealed no trend. These results show a shift towards application-focused work for eDNA-based assessments but also reveal this field to still be developing. In this transitional phase, practitioners need to ensure consistency and data comparability for long-term monitoring programmes.